Lafayette LR-9090 series / Setton RS 660 series Repairs & upgrades

K7sparky

AK Subscriber
Subscriber
Where this came from:
I started keeping notes for myself on LR 9090 referbs and repairs about amp number 3 just to remember what I had found and done. The latest 9090 I did, I updated and combined my notes and when I finally got a RS-660 I got serious about organizing this mess.

One Beg
If you have a good RS 660 schematic please do a GOOD scan and submit it to the AK data base and PM me. The 2 different RS 660 SM floating around both have poor quality schematic scans and the center is missing from them both. I have sent an updated scan of my LR-9090 SM and a SAMS LR 9090 manual (along with 1.5G of manuals, brochures, catalogs and 70s dealer mailers) to the database so they will get posted as the volunteers have time. http://akdatabase.com/AKview/ To submit to the database see http://www.audiokarma.org/forums/showthread.php?t=349096

Errata

I have found quite a few mistakes on the RS-660 schematic at least compared to the 660 I have. The 9090 schematic has 2 errors I remember both on the PAs: If / when I get a good copy of the RS 660 schematic I will attempt an errata for it.
LR-9090 & SR 660
1) +50 volts is soldered directly to a NPN collector on 9090 PA heatsinks and wire wrapped to post 7 on 660 PA heatsinks not TB pin 2
2) The PA PC board layout position of VR1 and D2 are reversed from the schematic.

Observation
The most of the LR 9090 to LR1515 series used discrete transistors in the PAs. With an A suffix added to the model number they some had power modules for the PAs. The LR-5555 / LR-5555A both had PMs. The only difference I could see was the A had extra LEDs for Mode as well as the FM Stereo. The LR9090 never had a A or PMs

I reference Mouser part numbers when it seems appropriate / helpful. Digi Key is another small quantity friendly source with large inventory I highly recommend.

This thread covers what I do on my amps. If you have found other mods helpful or helpful tips, I hope you will share them. Please do not let mistakes I have made go unchallenged and thus propagated. I also will be going back after I get this all posted and editing mistakes I made.

This is broken it up to multiple posts under the same thread, no eye deer if that is good or bad.

Check back now and then as updates are added as necessary
 
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General or “at the git go”
Inspect clear plastic (Lexan) on wire wrap TBs. If Lexan has been sprayed with a polychlorinated cleaner (most any cleaner that does not say Freon) it will be cracked. Use a sharp tooth pick to put on a coat of 5 minute epoxy. When the working puddle starts getting thick, mix some more. The thick stuff will not run down the holes and cracks. Not a perfect solution, but the best I have found so far.

PCB of this period have traces that easily lift. Get yourself a good vacuum desolder station or at least a good solder sucker and practice a LOT on old PCBs before you mess your amp up.. Desolder wick is NOT my friend, and I have a good collection left from what I have tried. A good solder station with 700F tips both small and medium IS your friend. More modern PCBs are made with G10 Glastic base / substrate and hold the traces much better.

When I remove wire wraps I use a #22 unwrap tool and straighten the wires with smooth jaw needle nose pliers and sleeve them with size 20 Polyacrylate resin coated fiberglass sleeving. Probably a waste of time instead of cutting off excess. I do have #22 wire wrap tools, but prefer soldering to the TBs. I tin one side of the wire wrap post before soldering to them. Some of the amps had a type of shielded wire from the preamp to main amp that is hard to get to take solder. Sometimes I fight with it others just replace it with good shielded wire about the same diameter as the original.

#20 and #22 coated sleeving are used a lot.

A good selection of colors of small size heat shrink is handy. I get the 4’ lengths at Hamfests.

Incoming power cord needs to have the unswitched / chassis grounded through a resistor side marked with a little white correction fluid. Also add a little white make to the outlets on the back. If any of the power outlets on the back need to be replaced, use polarized sockets oriented wide side to white. Necessary? Sure makes me feel better.

If I remove PAs to repair the TBs or other areas, I scrub the TO3 sockets with degreaser and a tooth brush. Any time a board is removed it is cleaned with scrubbing bubbles and a soft brush with a final rinsed of deionized water. I try to keep away from pots, switches and tunable coils. The board is usually dried for several days in the sun or by a heat vent if it has pots, switches or tunable coils. The scrubbing bubble trick was learned from a Sperry Gyro Rep years ago when he was cleaning soot and goo off Gyro cards after a fire. I have used scrubbing bubbles on thousands of cards with out an issue, give boards plenty of drying time. When the board is dry, pots and switches get a SMALL shot of D5 Deoxit if they have an opening.

My digital capacitance / inductance meter top capacitance range is 600 mf. I measure most of the caps I remove and replace and relative few are bad. To me it is well worth the effort and minor expense to not have to find the few bad ones. The big power caps are tested and only a few have been replaced.
 
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Main PA boards and heat sinks​
It is a good idea to pop the heat sinks and clean the old Wakefield compound (white stuff) off the heat sinks, insulators, screws and transistors. Most will recommend using gloves as the binder in the compound is Beryllium and bad for you. Remove the screws from the bracket to the chassis on both heat sink assemblies. Remove the left channel (one with the protective relay) first and don't forget to loosen the screw holding the Forward Reference Voltage diode. Take pictures to help in reassembly and note transistor location. Any of the super degreasers and an old tooth brush work to get the last of the compound off. You may need to resort to an air compressor to get the compound out of the base and emitter socket connections.

When you reassemble and coat the insulators, what you are doing is filling the microscopic pores to improve heat transfer. That requires a vary thin (just visible) layer of grease with a fine binder and an extremely thin oil. Before I retired from xx the approved grease was GE Versilube G322L for small semiconductors. Any light silicon grease will probably be as good. If you have an old tube of silicon grease that drips a little silicon oil now and then, the oil works great. Remember just a thin coat on the insulator only.

Replace C5, C6, C11, C12. For C11 & C12 I also use 47 mf @ 63V instead of 2.2mf because I had a bunch of axial lead ones and early PCBs missed C12 so it was added on the bottom of the board and an axial lead is easier.

Left PA only replace C16 & change C18 from 47mf to 220 mf. The PA output goes to + rail at power on and may oscillate a little before settling out to zero. You can watch this by monitoring R30 (beside L1) before the protective relay picks up. C18 at 47 mf is not enough time delay on all units to keep from cycling the protective relay and causing a loud speaker pop. The Setton uses a 100 mf (C3) on the Security Unit for the delay and I change this to 220 also. Do not change the value C16 unless you want to change the protective circuit attack time.

Point of interest is the grounds on the PA assemblies. Some early units have black wire from a ground trace on top of the PCB to a solder lug screwed to the heat sink I have found no problems removing it. The ground G between TB 6 and 1 is from the preamp board. The ground G on the opposite end next to TB 4 is from chassis. On some units connecting these 2 on the PA causes a ground loop (lots of hum) others make no difference so I never jumper them.

The schematic shows the Forward Reference Diode D2 (mounted on the side of the heat sink) anode connected to the base of Q3 and cathode connected to the bias adjustment pot RV1. RV1 connected from the cathode of D2 to the base of Q4. On the PCB they are reversed. Electrically identical, but something to be aware of during trouble shooting.

Measure the output to the speakers with no speakers connected. If it is above 20 mvdc either polarity RUN / DO NOT WALK to EchoWars Sticky http://audiokarma.org/forums/showthread.php?t=5634. Read at least the first 3 pages and decide how to fix it. There is no offset adjustment in the LRs and RSs.

Set PA idle current
I use (2) ma meters so I can monitor both channels while setting the bias, probably not necessary. You need to leave it on for at least 1/2 hour and have the volume at zero. The wire you want to lift to insert your ma meter is the pink one that comes from the + 50V filter cap and is twisted with the white one from the - cap. It is looped over the hear sink and soldered to a collector on the component side of the PA boards. The Setton
+ 50V it is wire wrapped to P7 beside a NPN collector. On the earlier version boards it takes some doing to get one side of the meter to hook to the collector. The later boards have a test post there so it is easy. BTW the collector you take the wire from is the same as pin 2 on the board.

If you prefer to measure voltage across the emitter current balance resistors R 21 & R22 (0.47 ohm probably 5%) there would be 25 ma through each one and you need to measure both and average them. Yep it does drift around a bit but should average 11.75 mvdv.

The bias will drift a little and the pots are a little hinky to adjust, I use my fingers not a screwdriver. Some of the 9090s bias are stable when first adjusted and others take a few touch ups every 1/2 hour or so, but all seem to hold after adjusted.
 
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Main Power Caps​
Check large power supply capacitors (still installed and hooked up) with an external supply, hopefully with a current limit. The positive will be in the 40 ma range and the negative in the 30 ma range if all is well. The negative current on the RS-660 was 80 ma as the security board it has soaks up difference. You should see current go up and settle as you are increasing the voltage to about 53V. Unplug one lead and the voltage should decay not drop like a rock. This is a quick dirty test of the caps. If the unit has not been turned on for a long time, monitor voltage / current for several hours to several days. When the amp is powered up the +50V and -50V will be within 100mv and around 54V on the LR and 62V on the RS. The RS transformer secondary winding voltage is 90VAC with 119 VAC line voltage and the LR is 78.8 VAC. Both prints call for 77 VAC at 120 VAC line. Both have the same 15K MFD at 63V caps. The Setton caps are closer to the rating than I like, but who can argue with 40 years of service and still working fine.


Power supply card​
Change C6 from 220mf to 1000mf, change C7 & C8. Change D1 to Schottky (1N5819 or similar). Take a close look at R1 & R2. I have found those resistors on some units that have uninsulated ends and if they bend a little and touch the D1 or D2 heat sinks you will be repairing burned traces. On the Setton add C6 & D1 if you are going to change to a LED light bar that will power off pin 13.

Tuner / low voltage board​
Replace 12 volt supply control zener (D11) with selected 1 or 2% unit for lowest THD on HA 1196 (FM stereo demodulator) curve. Target zener voltage for the 9090 is 13.1V (I use 13V 1/2W TXZ13C-TR Mouser 78-TXZ13C) to get 12.3 to 12.6 volts VCC on pin 1 of the HA 1196. This is the target voltage of every quality amp of the time period as they all used the same Hitachi chipset.

Replace C69, C70, C121, C122, C123, C124, C125, C126, C127 with equal or higher values. I use 220 mf for C121, C122 & 123, leave C 124 & 5 at 2.2 mf, 470 mf for C69, C126 & 7, leave C70 at 220. The Setton does not have the NE 545B for internal FM Dolby decode so does not have C70. Dolby FM is a nonissue, it never caught on and was dropped soon after it was announced.

Replace R142 with 30 ohm 5W (Mouser 280-CR5-30-RC) and R143 with 200 ohm 5W (Mouser 280-CR5-200-RC) to unload 18 volt regulators. I leave the leads long and use #22 sleeving to keep the heat off the PCB. When powered up I measure the voltage across R142 and R143 to derive the 18V supply currents. If all is well the positive will be about 19V @ 198 ma and the negative will be about 19V @ 42ma. If current is much higher there is a bad cap to ferrate out. The higher resistance also helps a little in saving traces from shorted components. The resistance values are what I use, a bit higher will not matter, just check the voltage on the regulator end of the resistors during operation to make sure it is high enough to keep the regulators happy.
 
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Replace burned out bulbs or modify Dial light bar to LEDs​

This modification started life on a carcass 9090 I was putting back together and needed a dial light bar. The first one was made from PCB material and the second folded aluminum on a brake. You need somewhere around 3/16” Plexiglas to transmit light to the dial and meters and be thick enough to drill into. I liked the look so much I have modified all my 9090s, one LR 120DB and the one Setton RS 660. LEDs will work with the original Plexiglas, but looks better without the lamp holes in the original. Also the red meter LEDs and Blue dial LEDs bleed over with a continuous Plexiglas.

I tested a lot of LEDs to find ones with good dispersion and intensity. I use all 20 ma rated T 1 ¼ LEDs. The voltage varies with color. For the LR-9090 & modified RS-660 the DC on pin 13 of the Power Supply card is between 9 & 10 volts. What I settled on was 3 ea blue VCC VAOL – 5GSBY4 (Mouser 593-VAQL-5GSBY4) in series with 1 ea red Avago Tech HLMP-ED80-K0T00 (Mouser 630 – HLMP –ED80 – K0T00). This combination requires no resistor for dropping voltage. I use 4 sets in parallel and current is 20 to 40 ma per set. Yep 40 ma is 2X rated so they are brighter.

EDIT:D
I've just rethought my LED light bar modification. One of the clan that has been mostly on for over a year had several of the blue LEDs out. I replaced them and the others looked dim by comparison so replaced then as well. Tried a new red and there was no difference in brightness. The blue LEDs do not put up with over current well in the long haul as well as the Red ones I used.

There is a good read at Digi-key on LED failure: http://www.digikey.com/en/articles/techzone/2011/nov/understanding-and-preventing-led-failure It basically says "Hey Dummy the spec is there for a reason" Should have studied LEDs more before "over revving " the LEDs. Did not know LEDs slowly loosing light output when abused was a normal failure mode.

The bar has 4 sets of LEDs and ran 120 to 150 mA or about 1.5 to 1.9X specification current and as it turns out caused loss of intensity of blue LEDs. Paralleling 2ea 1/2W resisters gives plenty of range to limit current to a total of 80 mA. The voltage drops at pin 13 as the current increases so a bit of testing is required. So far a combinations of 2ea of a combination 18, 27, 33 & / or 47 Ohms has worked OK. On future rebuilds I will not be changing D1 to a Schottky or increasing the value of C4. Your selection of LEDs will drive your requirement.
END EDIT:yes:

A #9 drill bit works great for a T 1 ¼ hole. I set the drill press to limit a little mote then the LED length. The Plexiglas is secured with (2) 4-40 screws. I thread the Plexiglas and clearance hole the metal back. Note in the pictures the 660 Plexiglas extends to the right side to illuminate the Security Panel, while the 9090 extends only to the end of the dial. If you get the LEDs too loose a little “Tacky glue” or low temp hot glue will help. Drilling too low and having the hole break into air does not seem to be a problem.

The wire is #30 wire wrap wire as I have it still around from the good old wire wrap days. Use whatever small wire you have. The glass sleeving is size 20 and the black insulation on the LED to LED leads is stripped from old Romex and slit with an Exacto knife.

All LEDs are installed cathode right looking down on the back on the bar.

The front edge of the plexiglass is back cut at 45 degree and coated white (I use white out) to reflect the light down. Also coat the end toward the meters so the blue will not bleed to the red for the meters. I use a 10” compound miter saw for the Plexiglas most of the time. A table saw also works OK.

The RS-660 meter light channel Plexiglas was broken so the replacement was whittled out on 1/8” material and the side towards the dial is coated white. I did not see enough change in light transmission to the meters to justify replacing good original light channels. If you need to make one I can supply more information on how I made it.

EDIT
Just made a few meter light channels out of 5/16" material and the difference in red transmission and blue block for the meters is worth the effort (IMHO) if you are using different color for the meter
End EDIT:thmbsp:

If you like the original bulb look, wedge base bulbs are available and a little solder paste (NOT acid) will help soldering on the pig tails. 14 volt 0.27A are bright enough and should last well. I was using Chicago Miniature 194 (Mouser 606-CM194) before I converted to LEDs.

RS 660 panel lights​
The original T 1 ¼ 6.3V 35 ma bulbs are a bit hard to find. I had a bunch of LEDs left from testing on the original LED dial light bar. I had used all T 1 ¼ 20 ma LEDs. Testing LEDs on the 660 front panel, they were all TOO bright anywhere close to design current. A decade resistance box was used to adjust brightness. The resistance can be added in series with the LEDS or change the resistors on the TBs.

Note: the RS-660 print is wrong for the FM Stereo Multiplex light. It is 12V from wire 29 on the Pre Amp unit PSPA028COX. If you are changing resistors it is R30 on the receiver board. I just added a 47K in series with the red LED Avago Tech (Mouser 630-HLMP-ED33-SV000)

Power On LED power was moved from the AC 7.5V pin 7 to 13 on the power card. On standard RS 660 pin 13 is open (see the LED light bar modification for DC to pin 13). AC on pin 7 will :DEDIT need a diode in series with the LED - LEDs are diodes but have around 5V PRV see the above edit on abusing LEDs).:eek: I used the same red LED and resistor as on FM multiplex. If you choose to leave power from pin 7 you might need to alter the series resistor to keep current within the LED rating.

Speaker light power is the -18.5 volt supply (LEDS cathode to red wire). I used green Avago Tech (Mouser 630-HLMP-CM34-X1000 with 13K series resistor .The clear (that has a hint of blue) Lite-ON (Mouser 859-LTW-2S3D8) looked good with 18K series as did the yellow Optek (Mouser 828-OVLGY0C9B9) with 13K series. The series resistor sets the brightness and is a personal matter of taste.

Diffused LEDs might be a little better than clear if you are buying them, with the low LED current the clear I had on hand worked fine.
 

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more LED light bar details
 

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Power Switch

Remove power switch dissemble, clean with scrubbing bubbles, lube actuator, replace power contacts if necessary. Look at the amount of contact material left compared to the NC set that dumps the protective relay in the off position. Do NOT file or burnish the switch contacts. The rough contact surface is beneficial on closing. Add an ice cube relay for power transformer, switched outlet on back and protective relay release. The power switch now only operates the small relay and the NC contacts can be used for replacement for the NO power ones if necessary.. If you plug too much into switched power outlet or something in the amp shorts all you blow is an easy to buy relay, not an impossible to find OEM switch. A 4PDT with a 120 VAC (example Omron LY4-AC120 Mouser 653-LY4-AC1) coil ice cube works fine for the transformer inrush on the 9090, but will weld contacts on larger power transformers like the LR 120DB. A DPDT ice cube is used on those. The DPDT is the same form as the protective relay but 2 pole and a 120 VAC coil instead of a 24 VDC coil. Example Omron LY2-AC1 (Mouser 653-LY2-AC1)

Add MOVs on transformer, new relay.

Separate file with lots of pictures and details is or will be shortly available and should be adapted to all makes of the old monsters to save power switches.
 
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Peek & tweek AM, FM & FM stereo​

The Lafayette and Sams manuals are a bit different on tuning the radio portion. Either works fine for me. The Sams says “Courtesy of Lafayette Radio Electronics” Why they are different? No eye deer.

I have noted that neither the 76KHz adjustment nor the Separation adjustment has never needed touching. Maybe just lucky

The AM & FM front ends always can use a bit to a lot of tweeking, however the reception out here in the weeds is just fine before the setup. So if you do not have the test gear to do it you will not be missing much. You can use a station at either end on the dial for getting the dial tracking set.

Has anyone tried an AC voltmeter on a tape out for peaking the rest of the front end?

Expanded Rx tune up see post 58
 
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General PA repairs
Replacement 2S power transistors are a bit hard to find and expensive. The SK, NTE replacement are also a bit spendy and any old s**t they can find. I have been studying transistor curves and choosing replacement transistors for years and my latest general replacements are
\MJ21196G NPN and MJ21195G PNP
You might like MJ21194G NPN and MJ121193G PNP also.
They are 250 volt, 16 amp 250 watt and the G is a TO3 form. They are available in other packages with different suffix letters.

Both pairs have identical ratings, but slightly different curves. They are available from Mouse and others at low cost.

For drivers I am using MJE15032G NPN & MJE15033G PNP. They are250volts amp 50 watt TO 220 style 1 (BCE)

If I replace any power transistors on a heat sink I replace all old part numbers with new complementary pairs. Do NOT mix different transistors between different complimentary pairs.


Repairs on one Setton RS-660 PA

I spent 3 days fighting with the right channel PA from my new Setton RS 660. Someone had been here first, always a bad sign. There was a burned off trace from R23 / 24 to L1, R15 was blown and a number of lifted traces from too much heat while someone was playing around. The original Q2 & Q3 2SD381 had been replaced with 2SC2073 and Q4 2SB356 (complement to 381) was replaced with 2SA1930 not complementary pair with 2SC2073. The 100 ohm bias pot RV1 was flaky and around 260 ohms. I got a great education about forward reference diodes (D2) as it was swapped with RV1 on the board layout compared to the schematic.

BTW D2 is a STV-4H and is 4 diodes in series in a single package. The STV-4H is speced 2.10V to 2.36V at 7ma. In a pinch I would guess using 4 silicon diodes in series would work, but the bias might drift a little more.

The PA was removed to the bench and powered with lab power supplies with adjustable current limits to keep it from letting the magic smoke out while trouble shooting. I have no excuse for not using a scope off the bat to find the darn thing had a high frequency oscillation. Hind sight is always 20 / 20. If you do not have a supply with adjustable current limit try a 100W bulb in series with one of the 50V, put ½ or 1A fuses in series with both 50V leave and use jumper the amp power out to the board. This is not a place for a nuwbie to go on an adventure! Tonto say UGH much magic smoke and fried fingers.

When the PA was returned to service in the amp, 1A fuses were add in series with + and – 50V in case of problems. They will become permanent and changed to 3A (200 watt 70% efficiency) after a month or so of driving some 12” or15” CVs.

I replaced Q2 & 3 with MJE15032G and Q4 with the complementary MJE15033G, but oscillations remained. C4 15Pf Q2 base to collector was removed and measured 17Pf. C19 & C20 were also in spec. Increasing value of the 3 caps had no effect on oscillation. The components on the board in the signal path were verified. The Hfe of the MJEs are in the ball park with the original. I could find no curves for the original transistors to compare.

Output transistors were changed from original 2Sxxxx to SK & NTE subs and to MJ21196G NPN and MJ21195G PNP which were left in place. The solder around several TO3 socket connections looked a little gray so all TO3 socket pins were resoldered. An interesting exercise, but no banana.

The oscillation was stopped by adding a .005 MFD from the collector of Q2 to ground. As an aside .001 almost stopped the oscillation, but not quite. My SWAG at the cause of oscillation is leakage caused by too much soldering heat diffusing contaminants into substrate. Some judicious scraping with a dental tool and a bit of conformal coating might also have worked.

If anyone cares the oscillation frequency was 162.7 KHz. With the output filter R29 & C8 removed the frequency increased to 769 KHz about the same amplitude. With C8 value doubled the amplitude (EDIT 2-14-23 Don't recall how the amplitude varied END) and frequency went down to 113 KHz. HP counter and Tek scope.

If you need to replace Q2, Q3 or Q4 on the PA, replace all 3 unless you get an exact 2Sxxx.

During this repair I started reading EchoWars Sticky “Amplifier Distortion, DC-Offset and You” http://audiokarma.org/forums/showthread.php?t=5634 . I was sorry I had not read or thought about this years ago. I’m up to about page 200 and will continue. If you haven’t read at least the first 3 pages, STOP and do it NOW!

I did use a pair of EchoWars favorite ZTX795A to make a 2SA798 (see pictures) trying to get ride of the 570 mv output offset after curing the oscillations, but that did not help. The final solution to the offset was defluxing the solder side and washing the board with scrubbing bubbles. Removing the .005 cap got the oscillations back after the offset was cured so it is there to stay. The offset now drifts between 2 and 8 mv.

Well that’s about it for now. I did not cover 2 oak cabinets I built for LR9090s, but will detail what I did if it will help anyone. I will be adding additional voltage readings to the LR 9090 schematics and eventually submitting it to the AK database. The RS-660 is a LR-9090 with different bells and whistles.

My friend that was a Lafayette store manager and repair tech told me the LR 120DB schematics did not have much in the way of voltage references as the product was not mature when LR folded. If anyone cares I can add a few and submit it to AK database. That would be from a universe on 1 working unit. Not something I would bet the farm on.
 

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Trying to get the pix interlaced with text is proving illusive.

Anyone give me some pointers??
 
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Power Switch 1

Murphy blew the power switch. OH SHIT!!!!! They haven’t made one in years. I am SCREWED!!

Maybe not. With a few parts and a little effort you can fix your amp better than original.

This is written based on a LR 9090 / Setton RS 660, but can be easily adapted to others. There are two Setton SM on the web and I sent a copy of my LR-9090 SM to the AK database so is will show up when the volunteers get to it. The Setton schematic will suffice for this exercise, however a bit of the center is missing on both copies. The Setton does not use the NC power switch contact to dump the protective relay.

Disclaimer / gentle warning:
You can let the magic smoke out of a lot of parts and yourself if you are not careful. 120 VAC is not high enough to knock you off (violent involuntary muscle contraction to remove your offending digit from the potential source) if you get your fingers in the wrong place and you will fry like the old hot dog cookers. I am not sure if a GFI receptacle on your test bench will save you from stupidity, but it is a good place to start.
For the newbie, print this, take it and your amp to a tech, the life and amp you save will be your own.

Parts List:
Relay I use most of the time is a 4 PDT ice cube, but almost any small relay with a 120 VAC coil will do. I like the 21mm x 27mm x 35mm size Example: Magneticraft 782XDX1C-120V, Omron LY4-AC1, etc.

Amps with larger transformers (even the LR 120DB) – read higher transformer inrush current will need higher contact rating to avoid contact welding. A DPDT ice cube with a 120 VAC coil (like Omron LY2-AC1) worked fine on the LR 120DB after it welded the 4PDT. Smaller contacts in parallel would suffice for steady state current, but contact make / brake time differences between contacts on the first few cycles of inrush depending on where in the AC cycle the contacts make or brake occurs comes into play as well as the subtransient reactance of the transformer. Lets skip the engineering lesson and go to “use enough gun”.

100W bulb in a pig tail socket if the amp is dead not just intermittent bad switch.

2ea 120/130 VAC MOV: examples: Littlefuse V130LA10AP or V130L10, SIOV or EPCOS S14K130

A bit of wire, sleeving, solder and solder wick (if you can use the darn stuff, I can’t so a desolder station is my solution).
Any of the foaming bathroom cleaners.
Multimeter

You need a good soldering iron. DO NOT use a big soldering gun!!!!! You are saving BIG$ by DIY. Shipping the stereo somewhere for repair costs more than a good temperature controlled iron. Buy one!

OK let’s get to it.
1) Make sure the power / speaker switch is off. (If you need to be told to unplug it, this is not for you) Remove case, bottom, knobs and front panel. Take a few pictures if you need help remembering how it goes back together. You know the switch is in the off position and a close up on the back of the power switch shows the rotor orientation for reassembly. Take a few minutes and clean the inside of the dial glass and dial it has needed it for years.

2) Set the receiver on end with the power switch on the bottom. Be careful not to slop solder into the receiver. It is easy to do removing the power switch for cleaning and repair.

3) While you are inside replace the power plug with a polarized one or at least use some white out to mark white on the common side of the existing plug. That is the white wire in the receiver and has a resistor to ground. Now you can plug the amp in and be assured of AC common to chassis.


4) Take the nut off the front of the speaker selector power switch. The switch used to write this up for had a sealer on it so I cleaned the threads after taking the nut off.

5) Carefully not to slop solder (solder wick or solder sucker for me) into the receiver remove the wires from the power switch. LR 9090 has a small black ground wire and a small white wire to the N/C contacts for PA protective relay towards the bottom. The N/O contacts have a yellow wire from the power cord on one side and a red to the transformer fuse and brown to the switched power receptacle. RS 660 use different colors and does not have any AC outlets on the back panel or use the NC contact. Both LA & RS have a cap in silicon rubber boot across the NO contacts.

6) If the amp was dead, tape off all but the yellow wire from the power cord and red wire to the fuse on the power supply card. Now is the time to find out if the receiver has internal problems to fix or the switch just got tired. Hooked the 100 watt bulb in series with those wires (in series with the transformer primary).


7) Plug the amp cord into a power strip that is switched off. Turn the power strip on. If the amp has no other problems, 100 bulb will probably not glow and the panel lights will come on. A shorted diode, bad cap, shorted output transistor, etc will light the light. An open primary on the power transformer = no 100 W bulb on and no panel lights. Fix other problems as necessary and remember the part that dies may not be the part that kills. Power switch failure is a known problem of this breed. You DID check the fuse on the power supply card before you ever got this far. You need to put the relay in anyway as the switch WILL die without it.

8) Tip the switch assembly out only as far as necessary to access the nuts on the back of the switch. Carefully remove the 2 nuts and washers holding the power switch to the back of the wafer stack. Slide the switch off and put at least one of the nuts all the way on and the other on enough to keep the screw from falling out.

9) Note the mark on the rotor is aligned at 1. The switch is not glued and easily comes apart. The inside will be black and smoky around the NO contacts even if they have not failed. Take a picture. Carefully wiggle the contacts out. Use a tooth brush and foaming cleanser to clean up the inside of the switch. I have used the bubbles on BIG$$$ systems after fires and it is the best there is for soot and grease removal. Completely dry. Inspect the contacts. The power (N/O) are probably toasted. The PA protective relay contacts look like new. Install the good contacts in the power side and leave the other side empty. Use a little lube on the rotor if you like. Set the rotor so the power contacts are open (YEP the rotor mark will align with 1 on the back of the switch)! Carefully wiggle the case back together and make sure the mark is aligned with the1. Do NOT sand or burnish switch contacts, the rough surface is an aid when switching on.

The first thumb is my sloppy drawing
2dn is the switch as it is removed
3rd Switch interior and contacts have been cleaned with scrubbing bubbles. Well used, but serviceable contacts by cap and rotor pointer is at good PA relay contacts
4th is Contact from PA relay control moved to power on side of switch
 

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Power switch 2

10) Look around and see where you want to mount the new relay see picture for where mine is. Solder new wires on the 2 switch contacts long enough to reach the relay location. Test the switch with your ohm meter to make sure you got it together correctly. Install the switch on the wafer stack and tighten the nuts snugly. They are small so do not get carried away. Install the switch in the subpanel and tighten the front nut.

11) It is decision time. Do you want to keep a switched power socket on the rear panel? Do you want to keep the cap across the NO contacts for arc suppression? Do you want a relay socket?

12) The relays I used have 4 sets of contacts so I used a NO set for the switched socket, ganged 2 NO for the transformer and a NC set the PA relay control circuit. I do not reuse the cap as I think the MOVs are all that are necessary. One MOV is across the new relay coil to protect the power switch contacts. My relay is simply soldered no socket and wedged into place by the wire bundle. You can see the sleeving I used on the wires soldered to the relay contacts I used as a terminal board. Use some double stick tape or hot glue to hold the relay in place if you deem it necessary. A relay socket might fire your rocket.

13) Smoke test and put it all together.

14) Hook it up, crank it UP and It’s Miller Time!

Has anyone done this with a Triac? Something like a Littlefuse Q4025L6 (Mouser 576-Q4025L6) Rated 400VAC 25A RMS for highly inductive loads and tab isolated is over kill size and maybe too high a latching current. Yea olde Fluke gives around 7A on the 100 ms max / min, 25A to 30A on the 1ms peak for power on and 0.6A steady state at low volume. Data sheet is on Mouser. $3.40 is cheap!

Pix 1 Relay with buss wires (use as terminal strip) and sleeving installed. White coil wire goes to power neutral. The white and black wires on the NO contacts are for PA relay on LR 9090. The 3 commons contacts tied together go to power, the 2 NO ganged hook to red from Power supply card and outside NO is to brown for switched outlet.

pix 2 Relay installed. When finished soldering to relay cut off extra wire. Yellow is power from incoming line, red is to transformer fuse on power supply board brown to switched AC socket. The small orange and purple are the power switch contacts.

pix 3 New Relay installation complete. I now use heat shrink over connections.

pix 4 Second MOV installed on transformer primary on the Power supply board. White wire on MOV is run from neutral (white wire) on power cord. I put a bit of heat shrink to over the MOV neutral connection.

pix 5 Power switch back in place with wires for new relay
 

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Power switch replacement

This was done in a RS 660 before I got it so I know nothing of it's origin. It is just too good a repair not to share.

Pix 3 is of the switch that was in the RS when I got it and the one with the lever on it was a top closed switch from an old washing machine. Just removed the lever and it worked fine.

When I replaced the bad parts and trace on the right PA and installed it, the magic smoke left. Blew the fuse and welded the switch. First PA in one of these that has had that bad a problem. Covered in a post above.
 

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Thanks for sharing! Most of the electronics are beyond me, but I actually have a 220 disassembled for cleaning and new lamps. Here's a pic. Looks to take the typical Pioneer 8v300ma wedge lamps, not sure if that's different with a 660? I started veneering today, hope it comes out well. Not to clutter your thread, there is just not much info out there on these units and they all seem similar.
 

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Wow.
It's apparent you have put a lot of time and effort into this tutorial.
Hopefully it will help others. It is way too technical for my skills. lol
I am a Lafayette fan, bought a LR-9090 new in 1977 and I bought a used LR-120DB last year.
 
JT-3 the RS220 is a LR3030 with different bells & whistles. Same 8V lamp they all use. The CM is a little higher voltage and thus a little softer light and lasts a lot longer, does not bake the gray rubber as bad or tend to discolor the light bar Plexiglas as bad. If you haven't removed them yet, wiggle he gray rubber around a bit to help brake it loose and a little lube helps both out and in not to not tare the rubber or crack the plastic.

I read the thread on redoing the veneer and am planning to try that on the 660 cabinet. Take some pictures and any tips you discovered would help me and others.

Any of the scrubbing bubbles work great to clean up everything from face plates to cards. If you wash the electronics give the PCBs plenty of time to dry. Try to keep as much water as possible out of the switches. I have found that a shop vac blowing does a better job than a my air hose. Then just warm air like a heat register for a few days.

Consider the power switch mod. The originals are unobtainum and the relays are cheap. A shorted output could be the end of your PS. BTW does your power switch look like the picture of the one from the 9090?

The Settons belong here and hopefully we can all learn a bit.
 
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Wow.
It's apparent you have put a lot of time and effort into this tutorial.
Hopefully it will help others. It is way too technical for my skills. lol
I am a Lafayette fan, bought a LR-9090 new in 1977 and I bought a used LR-120DB last year.

The 4 pictures under my light replacement / LED light bar (post #5) are a Setton RS660, LR9090, LR120DB and the right edge of the Setton RS 660. Got my 120 last year as well and it had a mystery card between the preamp and PA. I drew up the circuit and it made no sense. Also have searched the numbers on the board to no avail. A friend that was a mgr of a Lafayette store had never seen or heard of it either.

The 9090 light bar was just shortened a little and put into my LR5555A

I can share the voltage readings I got on the 120 if you ever need them. Only a universe of 1 so not too much cross checking. They are not in the service manual as the unit was too new to get much included when Lafayette folded. BTW I see the SM I submitted is in the AK DB now.

The power on relay I used in the 120 is a DPDT and I used them in parallel and left the protective relay trip on the power switch as original. Bigger transformer = higher inrush = welded contacts on the 4 pole. I need to get inspired this winter and do a TRIAC instead of the relay. I ordered some TRIACs when I had to get some low noise transistors for a 9090 mike amp that had Q3 braking down causing crackles in both speakers.

I love the great stuff on this forum that can be found searching and just reading the old posts.

The light bar in the 120DB has tin foil between the 2 ea plex to the meters and the plex to the dial to keep out color bleed. If you want to build 1, I took plenty of pictures.
 
I actually used some blue plastic sheeting on my light bar to lessen the yellow/orange glow...I was hoping for a blue tint but ended up with more like a grey, but it was less glaring at least.
My 120DB does have a faulty off/on switch. I've used a switchable extension cord to bypass the switch. Looks dorky but it works.
I did measure the dc offset and it wasn't bad, I got 19mv on the right side
and 23 mv on the left side.
 
I actually used some blue plastic sheeting on my light bar to lessen the yellow/orange glow...I was hoping for a blue tint but ended up with more like a grey, but it was less glaring at least.
My 120DB does have a faulty off/on switch. I've used a switchable extension cord to bypass the switch. Looks dorky but it works.
I did measure the dc offset and it wasn't bad, I got 19mv on the right side
and 23 mv on the left side.
You are in luck! The LR-120db has redundant switch sections and hopefully the second set have never been used. I highly recommend you use a power on relay to save the second section. If I get a TRIAC mod done I will post it.

I am still trying to figure out how to get a picture in the text instead of an attachment.

The power switch is upper right, The transformer power wires are on the bottom of the outside terminals. The set of contacts above it are the same. The contacts for the protective relay dump are in front and all you can see in the picture is the white wire from the NC contacts.

The amp was built by Luxman. You might find a power switch for a Luxman is identical.

Happy trails
 

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Caution about Setton case screw length

The case screws for at least the RS660 I have are 4 X 0.7 X 14mm. The 14mm is important in locations that have a PCB under the flange. Like front center. Too long and it grounds a trace on the board. Do not remember what I had to repair just now, but a too long screw before I got it caused the problem.
 
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